1. Field of the Invention
The present invention relates to radar level gauging systems, and particularly to a radar level gauging system providing improved accuracy in gauging the level of a surface of a fluid stored in a container, when the surface is close to the bottom of the container as well as a method for such gauging.
2. Description of the Related Art
Radar level gauges are commonly used today for measuring the level of the surface of a fluid kept in a container, such as a tank, by transmitting a microwave signal towards the fluid surface and receiving a reflected microwave signal from the fluid surface, whereby the level of the fluid surface can be determined. It is important for users to achieve accurate readings of the fluid level close to the bottom and also to detect when the container is empty.
One problem is that, especially in the case when the fluid has a low dielectric constant, the main part of the reflected signal is reflected from the bottom of the container and not from the surface of the fluid. This may lead to a distorted signal, unless the filling level of the fluid is high, because then the signal reflected by the bottom will be absorbed by the fluid. This problem increases consequently when a low level of the fluid is prevalent.
Another problem is that there almost always is a layer of a by-product, such as water, in the bottom region of the container, which arises due to separation, condensate etc. Also the interface of the by-product will give a stronger reflected signal than the surface of the fluid, when the dielectric constant of the by-product is relatively high.
Previously known radar level gauges, therefore, may have limitations when it comes to measuring the level of a fluid close to the bottom of the container in which the fluid is stored.
Accordingly, it is an object of the present invention to provide an improved method for measuring a level of a surface of a product stored in a container allowing for measuring the fluid level close to the bottom of the container as well as detecting when the container is empty.
This object is achieved through a method comprising the steps of: transmitting a microwave signal towards the product surface using a radar level gauge arranged above the product surface; receiving in said radar level gauge a microwave signal reflected from the product surface; determining in a calculation unit a measured value of the product level based upon the received signal; comparing the measured value of the product level with a predetermined product level value; and determining the product level using a second level gauge arranged close to the bottom of the container when the measured value is below the predetermined product level value.
Another object of the invention is to provide an improved level gauging system for measuring a level of a surface of a product stored in a container allowing for measuring the fluid level close to the bottom of the container as well as detecting when the container is empty.
This object is achieved through providing a level gauging system for measuring a level of a surface of a product stored in a container comprising: a radar level gauge arranged above the surface of the product and arranged to transmit a microwave signal towards the product surface and receive a reflected microwave signal from the product surface; a calculation unit arranged to determine a measured value of the product level based upon the received signal; means for comparing the measured value of the product level with a predetermined product level value; and a second level gauge arranged closed to the bottom of the container and arranged to determine the product level when the measured value is below the predetermined product level value.
Still other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.